Final answer:
The activation of cytotoxic T-lymphocytes by interleukin 2 from helper T-lymphocytes is true. MHC II complexes are found on antigen-presenting cells, not most body cells, while MHC I is present on nearly all nucleated body cells.
Step-by-step explanation:
The statement regarding the activation of cytotoxic T-lymphocytes (CTLs) is true. During their activation, CTLs indeed require a second signal which involves stimulation by interleukin 2 (IL-2) released by helper T-lymphocytes (TH cells). CTLs, which are CD8+, are part of the adaptive immune response and are capable of directly killing infected cells, especially those harboring intracellular pathogens such as viruses. On the other hand, helper T cells or CD4+ cells, help orchestrate the immune response by releasing cytokines that activate other immune cells.
Regarding the provided options for misconceptions on T cells, statement c is false. MHC II complexes are present primarily on professional antigen-presenting cells (APCs) like dendritic cells, macrophages, and B cells, not on 'most body cells'. Conversely, MHC I molecules are present on almost all nucleated cells of the body, not just immune cells. These molecules play a critical role in presenting peptides to T cells and alerting the immune system of the presence of pathogens.